Manuscript received May 6, 2012; final manuscript received September 15, 2012; published online October 15, 2012. Assoc. Editor: Quan Wang.The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

Propagation of Rayleigh traveling waves from a gas on a nanotube surface activates a macroscopic flow of the gas (or gases) that depends critically on the atomic mass of the gas. Our molecular dynamics simulations show that the surface waves are capable of actuating significant macroscopic flows of atomic and molecular hydrogen, helium, and a mixture of both gases both inside and outside carbon nanotubes (CNT). In addition, our simulations predict a new “nanoseparation” effect when a nanotube is filled with a mixture of two gases with different masses or placed inside a volume filled with a mixture of several gases with different masses. The mass selectivity of the nanopumping can be used to develop a highly selective filter for various gases. Gas flow rates, pumping, and separation efficiencies were calculated at various wave frequencies and phase velocities of the surface waves. The nanopumping effect was analyzed for its applicability to actuate nanofluids into fuel cells through carbon nanotubes.

(a) Dependence of flow rate through the activated nanotubes on the simulation time for various wave frequencies: 1011–1013 Hz. (b) Average flow velocity versus time, for various wave frequencies (1 atom/ps = 2.4 × 10−4 sccm).

The dependence of the maximum flow rate on the frequency of the traveling wave for three different nanotube lengths L = 50, 100, and 150 Å, for two oscillation magnitudes: 1.5% and 3% of the nanotube radius

The gas-separation effect strongly depends on the atomic masses of gases, wave frequency, and phase velocity of the surface wave: (top) the initial position of 128 gas atoms inside the carbon nanotube (64 helium and 64 hydrogen atoms); (bottom) position after 35 ps of generation of the Rayleigh (traveling) waves on the nanotube surface: only helium atoms are left, and all hydrogen atoms are gone. (The direction of the surface wave is from left to right.)

Number of helium and hydrogen atoms that moved to the right side (the direction of the traveling surface wave) during the nanopumping by activated surface waves on the nanotube surface. Initially, 128 gas atoms were randomly placed inside the {15 × 0} carbon nanotube (64 helium and 64 hydrogen atoms). After 35 ps of generation of the Rayleigh (traveling) waves on the nanotube surface, almost all the hydrogen atoms were removed by the interaction with the walls, and only helium atoms are left.

Gas-separation effect for two gases placed outside the nanotube: (top) initial positions of 256 gas atoms outside the carbon nanotube (128 helium and 128 hydrogen atoms, open symbols are for helium and full symbols—for hydrogen); (bottom) position after 140 ps of generation of the Rayleigh (traveling) waves on the nanotube surface, showing a separation between them: the helium atoms mostly move to left (opposite direction to the wave movement), and the hydrogen atoms move to right direction (the wave direction)

Weaker gas-separation effect found for two gases placed outside the carbon nanotube. The solid symbols are for the hydrogen full flux in the direction of the wave (from left to right in Fig. 6). The open symbols are for helium atoms showing that helium atoms are moving backward, in opposite direction to the wave movement.

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